1. Technical Field
The present invention relates to a paper feed mechanism that conveys recording paper by means of a paper feed roller and paper pressure roller, and to a printer.
2. Related Art
A paper feed mechanism that conveys recording paper while pressing the recording paper by means of a paper pressure roller to a paper feed roller that is driven rotationally by a motor are commonly used in roll paper printers and other types of printers. Paper feed mechanisms of this type are taught in Japanese Unexamined Patent Appl. Pub. JP-A-H05-92627 and Japanese Unexamined Patent Appl. Pub. JP-A-H07-323623.
Japanese Unexamined Patent Appl. Pub. JP-A-2004-269176 teaches a paper feed mechanism that uses a torsion bar to press the paper pressure roller to the paper feed roller.
Self-centering mechanisms are commonly used with paper feed mechanisms in order to balance the contact pressure of the paper pressure roller to the paper feed roller in the widthwise direction, which is the same as the axial direction of the rollers. The self-centering mechanism causes the paper pressure roller to rock on its width wise center, and causes the paper pressure roller to press against the paper feed roller with uniform pressure in the axial direction.
However, when the center of the paper feed roller found by this self-centering mechanism is offset from the widthwise center of the paper transportation path, one side of the width of the conveyed recording paper will be held between the rollers with greater pressure than is applied to the other side. When this happens, the paper feed force applied to the right and left sides of the recording paper will not be the same despite the self-centering operation of the self-centering mechanism, and the recording paper will therefore become skewed and proceed at a bias to the paper feed direction, and possibly lead to a paper jam.
Roll paper printers that have the paper feed roller disposed to an access cover that opens and closes a roll paper compartment, have the paper pressure roller disposed to a fixed position on the paper frame side, and are configured so that opening the access cover also opens the paper transportation path are also known from the literature. In roll paper printers of this type, however, the paper feed roller and the paper pressure roller are disposed to separate parts, and the widthwise centers of these rollers are easily offset from each other. As a result, the recording paper can easily become skewed despite there being a self-centering mechanism being used to prevent skewing.